<<Nigel has the OPA 627, ELNA Silmic 470UF and the 2.2uF polyprops in his Chiarra and it would be interesting to learn if he found the same major improvement these components brought about as I did. PinkFloyd >>

Yes, installing the OPA 627's & upgrading the caps brought worthwhile musical improvements. The OPA 627 raises the performance of the amp unquestionably. I believe Shaun Williams, the amp's manufacturer, highly rates this combination. Personally, I used to like the OPA 2604, maybe a bit too warm sounding but good value nevertheless, it always allowed enjoyment of the music but seemed to mask fine details. I forget the identities of all the opamps we tried but recall the OPA 2107 was very musically satisfying. I believe the OPA 627 is quite expensive as well but it does pay dividends with musical rewards. I've never heard the Prehead so can't pass comment but expect it to be a fine sounding product. I trust Ross & respect his opinions, if you read his posts on this and other sites he doesn't have any agendas, musical satisfaction is his goal he's not part of Team this or Team that, I also know he uses some of the finest source components built by man so if he says product A is better sounding than product B it probably is. But, I think I'm correct in stating, even with the finest sources, we are not talking about major differences & sometimes all this comparison can detract from enjoying the music. But it's great fun & certainly useful to potential purchasers of headphone amps. Having said that, I do have an agenda, I'm part of Team Chiarra & if our favourite is being tested against the world's finest we want her sounding her best. We want to win, so if you need any opamps Ross, we'll send you some down.